Interstellar Comet 3I/ATLAS Grows Brighter and Greener as New Telescope Images Track Its Approach

Washington, D.C.; December 13th, 2025.

New telescope imagery released by federal space agencies confirms that Comet 3I/ATLAS, only the third confirmed interstellar object ever observed passing through our solar system, is becoming progressively brighter and exhibiting an increasingly green hue as it continues along its trajectory; the observations come directly from spacecraft and ground-based survey systems operated by NASA and partner agencies, and they document measurable changes in the comet’s activity rather than speculative modeling or visual interpretation alone.

According to NASA, Comet 3I/ATLAS was first identified by the Asteroid Terrestrial-impact Last Alert System, known as ATLAS, a NASA-funded sky survey network designed to detect near-Earth objects and transient celestial bodies; archival data later confirmed that the object originated outside the solar system, placing it in the same rare category as ‘Oumuamua in 2017 and 2I/Borisov in 2019. The classification of 3I/ATLAS as interstellar is based on its hyperbolic trajectory, meaning its path cannot be explained by gravitational interactions confined to our solar system.

Recent imaging released by NASA shows that as 3I/ATLAS moves closer to the Sun, its coma, the cloud of gas and dust surrounding the nucleus, has grown more pronounced; brightness increases recorded by multiple instruments indicate heightened outgassing, a process in which volatile materials sublimate directly from solid to gas when exposed to solar radiation. This outgassing is a standard cometary behavior, but its rate and chemical signature are of particular interest when the object originated beyond the Sun’s sphere of influence.

The increasingly green coloration observed in the comet’s coma is not a visual artifact or digital enhancement; NASA explains that the green hue corresponds to emissions from diatomic carbon and cyanogen gas, compounds that fluoresce when energized by ultraviolet radiation from the Sun. These emissions are commonly detected in comets, but their visibility depends on activity level, viewing geometry, and the sensitivity of the observing instruments. In the case of 3I/ATLAS, the enhanced green glow indicates that the comet’s nucleus is actively releasing carbon-based gases as it warms.

High-resolution imagery captured by the NASA Hubble Space Telescope provides additional confirmation of this activity; Hubble observations allow scientists to isolate fine structural details in the coma and measure how gas and dust expand outward from the nucleus over time. These observations are not interpretive summaries but direct records of reflected sunlight and gas emission spectra, forming the basis for chemical and physical analysis by planetary scientists.

Beyond Earth-based and near-Earth instruments, NASA has confirmed that other spacecraft have contributed observational data as well, including wide-field imaging systems designed to monitor transient solar system objects. By comparing images taken at different times and from different vantage points, researchers can verify that the changes in brightness are intrinsic to the comet itself rather than the result of changing viewing angles or atmospheric interference.

Despite its growing brightness, NASA has stated that Comet 3I/ATLAS does not pose a threat to Earth; its trajectory keeps it at a safe distance, and its passage is being tracked continuously using established planetary defense monitoring protocols. The significance of the object lies not in risk assessment, but in scientific opportunity. Because interstellar comets formed around other stars, their composition offers a rare physical sample of material from outside the Sun’s natal environment.

Scientists with NASA emphasize that each confirmed interstellar visitor provides a comparative data point for understanding how planetary systems form and evolve across the galaxy; differences in ice composition, dust grain structure, and gas emissions can reveal whether the processes that shaped our solar system are common or unusual on a cosmic scale. The active behavior of 3I/ATLAS, including its increasing brightness and gas release, gives researchers a valuable window into these questions.

As observations continue through December and into the coming months, NASA expects to refine measurements of the comet’s rotation, activity cycles, and chemical output; additional imaging will help determine how rapidly the nucleus responds to solar heating and whether its behavior differs in meaningful ways from comets formed within the solar system. For now, the confirmed brightening and green emission stand as direct, observable evidence of an interstellar object reacting to its first close encounter with our Sun.

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Sources

• NASA, official comet tracking and image releases for Comet 3I/ATLAS
• NASA Hubble Space Telescope, high-resolution imaging observations of Comet 3I/ATLAS
• ATLAS Survey Program (NASA-funded), discovery and orbital classification data for Comet 3I/ATLAS